Microphone



Aug. 8, 1939.

H. JACQBY lg-r AL MICROPHONE Filed March 9, 19:56

ATTORNEY Patented Aug. 8, 1939 MICROPHONE Hans Jaco'by, Finkenkrug, East-Havelland, and "Hans Panzerbieter, Berlin-Haselhorst, Ger- 'many, assignors to Siemens and Halske, Aktiengesellschai't, 'Berlin-Siemensstadt, Germany,

a corporation of Germany Application ltiarch 9, 1936, Serial No. 67,808 I v In Germany March 12, 1935 Claims. i This invention relates to anew and novel type of microphone. f c

Microphones are known comprising fixedelectrodes and loose granulated carbon and in which 5 the fixed electrodes are so arranged in deep cavities that the free outer surfaces thereof are completely covered with the contact powder; The electrodes are arranged lateral to the path of granules and extend at right angles to said path. It happens hereby that the current threads coniing from the limiting surfaces of the path of granules impinge only on a definite comparatively small region of the electrodes. This condition entails a high current'densit'y at the electrodes;

' 1 Owing to this high current density there occurs through the electrode a large drop of the direct voltage this part of the direct potential being not sufficie'ntly controlled by the movement of the diaphragm, and consequently it remains substantially without influence upon the delivered alternatingf voltage. Thisjhigh current density however causes a strong noise potential of the micro- Phone. Y

The present invention relates to a microphone "of the type above described and aims at overcoming the said'drawbacks. This is accomplished in accordance with the invention in' thatprovision is made'so that the current threads starting from the pathof carbon granules have, up to all places joi'the electrodes, the same length or at least approximately the same length. In addition the effective faces of the electrodes are substantially larger than the actual crosssection of the granulated carbon which likewise insures a.

current density as low as possible.

In the drawing two embodiments of the invention are represented by way of example.

Figure 1' shows thecross section of a rectangular microphone, I 0 Figure 2 represents a top view of this micro phone,

Figure 3 shows the cross section of a round microphone,

Figure 4 shows the .top view of this microphone. In Figures 1 and 2, the electrodes l and 2 are arranged substantially laterally to the granulated path in cavities 3 and 4 of the casing 5 and this in such manner that the current threads 6 between the faces of electrodes I and 2 have approximately the same length from the path of the carbon granules. This is accomplished by having the outer surfaces oi. the electrodes I and 2 arranged'in a steep angle relative to the limiting edges of the path of granules. The microphone casing 5 is entirely filled with carbon granules,

the casing being completed by a diaphragm 'I,'a cover plate 8 and spacer rings 9, II), II, and II. The microphone casing may be constructed of metal in order that the heat delivery be as favorable as possible. In this case the inside must of 5 course becovered with a non-conducting lacquer to provide insulation for the carbon granules and also electrodes l and 2. Obviously, also other material of favorable heat conduction such as ceramic material may be utilized without depart- 10 ing from the spirit of the invention.

As compared with the rectangular shape of the microphone according to Figures 1 and '2, the microphone according to Figures 3 and 4 has the further advantage thatit can be usedin any position. The rectangular microphone however must be suspended always in such a position thatthe electrodes are vertical. In Figures 3 and 4,"the electrodes are designated by l3 and I l. The electrode l3 has an an- 0 nular shape and is mounted in a cavity 20. The electrode ll forms a central cylindrical body which has on one end face a circular recess or depression of semi-circular cross section. This recess'or depression is arranged in the manner 25 that it extends aboutthe limiting or-boundary edges I5 of the path of granulated carbon.

Item l6 designates the microphone casing, item I1 is the diaphragm, and I8 designates a cover plate. As seen in Figure 3 the current lines I9 30 extend over the same distance from the limiting edge I501 the path of granules to all places of electrode H. The same is also the case for electrode l3. In order to prevent the granules sticking together and forming a mass, the microphone casing may be provided with'an intermediate layer consisting of gauze or similar material such as is shown by item 2| in Figures! and '2: The object of gauze 2| is to maintain and insure uniform distribution of the carbon granules along 40 the diaphragm I in Fig. 1 and diaphragm I! in Fig. 3. For example, when the microphone happens to be in a vertical position, the carbon particles will not pack together with the result that the operation of the microphone will be independ- 45 cut of the position of the instrument. In fact, the constituent members of the texture of the gauze act as a plurality of containers or pockets for the carbon granules.

We claim: 50

1. A carbon microphone having carbon granules in contact with a diaphragm and electrodes arranged so that the current lines in the direction of said diaphragm through the path of the carbon granules between the faces of the electrodes are substantially the same length, comprising a diaphragm, a circular casing, a depending cavity located at the outer rim of said casing, a second depending cavity located at the central portion of said casing, carbon granules filling both depending cavities and the space within said casing, a ring-like electrode located within the rim of said casing, a second electrode located within said second cavity, the face of at least one of said electrodes presenting an angle which is steep with respect to the plane of the diaphragm and said casing, said diaphragm arranged for enclosing said casing and serving to retain said carbon granules'in position, the eflective surface of said electrodes being substantially larger than the cross-section of the carbon granules.

2. A carbon microphone having carbon granules in contact with a diaphragm and electrodes arranged so that the current lines in the direc-' the face of at least one electrode presenting an angle which is steep with respect to the plane of the diaphragm and said casing, said diaphragm arranged for enclosing said casing and serving to retain said carbon granules in position, the elective surface of said electrodes being substantially larger than the cross-section of the carbon granules.

3. A carbon microphone having carbon granules in contact with a diaphragm and electrodes arranged so that the current lines in the direction of said diaphragm through the path of the carbon granules between the faces of the electrodes are substantially the same length. comprising a diaphragm, a circularcasing, a depending cavity located at the outer rim of said casing, a second depending cavity located at the central portion of i said casing, carbon granules filling both depending cavities and the space within said casing, a ring-like electrode located within the rim of said casing, a second electrode located within said second cavity, the face of'at least one electrode presenting an .angle which is steep with respect to the planeof the diaphragm and said casing, said diaphragm arranged for enclosing said diaphragm-to prevent said carbon granules sticking together.

4. A carbon microphone having carbon granules in contact with a diaphragm and electrodes arranged so that the current lines in the direction of said diaphragm through the path of the carbon granules between the faces of the electrodes are substantially the same length, comprising a diaphragm, a circular casing, a depending cavity located at the outer rim of said casing, is second depending cavity located at the central portion of said casing, carbon granules filling both depending cavities and the space within said casing, a ring-like electrode located within the rim of said casing, a second electrode located within said second cavity, the face of at least one electrode presenting an angle which is steep with respect to the plane of the diaphragm and said casing, said diaphragm arranged for enclosing said casing and serving to retain said carbon granules in position, the effective surface of said electrodes being substantially larger than the cross-section of the carbon granules, a gauze-like member interposed between said casing and said diaphragm to prevent said carbon granules sticking together, and a cover plate extending over the front of said diaphragm.

5. A carbon microphone having carbon granules in contact with a diaphragm and electrodes arranged so that the current lines in the direction of said diaphragm through the path of the carbon granules between the faces of the electrodes are substantially the same length, comprising a diaphragm, a circular casing, a depending cavity located at the outer rim of said casing, a second depending cavity located at the central portion of said casing, carbon granules filling both depending cavities and the space within said casing, a ring-like electrode located withinthe rim of said casing. a second electrode located within said second cavity, the face of said ringlike electrode presenting an angle which is steep with respect to the plane of the diaphragm and said casing, the face of said second electrode having a recess of semi-circular cross-section, said diaphragm arranged for enclosing said case ing and serving to retain said carbon granules in position, the effective surface of said electrodes being substantially larger than the cross-section of'the carbon granules.

HANS JACOBY. HANS PANZERBIETER. 

